Acoustic signal transducers



w. F. KNAUERT 2,927,978

ACOUSTIC SIGNAL TRANSDUCERS March 8, 1960 Filed Nov. 17, 1958 2 Sheets-Sheet 1 h/ INVENTOR. 7 firm/21') March 8, 1960 Filed NOV. 1'7, 1958 W. F. KNAUERT ACOUSTIC SIGNAL. TRANSDUCERS 2 Sheets-Sheet 2- 2,227,978 OU T C S AL TR NSQU EB William F. Knauert, Yonkers,.N.ii., assignor to So notone Corporation, Elmsford, N.Y., a corporation of New e nli sf on Nqvetnh r 958 Se i l 1!? 73 1 Claim ((1 11 i I This invention relates to acoustic signal transducers of'the type described in U.S.' Patent transduce acoustic signals into electric signals bri signals into acoustic signals, More particularl invention relates to miniature siz'ze transdu type, the volume dimensions of which should I aboutW f x x /2", so as to make it pos's 1e o combine two such transducers, one operating as a v phone and the other as areceiver, together operating components of a multi-stage transi' fier, into a minute volume fitting into a temple "of eyeglass frame or into a tiny casing fitting behind the outer ear or within the cavity of the outer ear ofthenser'.

In such acoustic signal transducers, an acoustic d1"- phr'agm is connected to" driveor be driven by a flat ferr magnetic armature or reed which is surrounded. by a spool with transducing windings and is arranged to vibrate between one or two pairs or1ose1ys aj posite poles of a ferromagnetic core for operation either as a microphone ,1 receiver in transducing vibrations of an acoustically excited'diaphragm into corresponding electric signals and vice. vers'a. For eflicient operation of such miniature transducers, the tiny flat reed must vibrate within a tiny,'flat central spool'compartment free from interference by the closely-spaced adjacent compartmentwalls. Miniature size microphone and receiver transducers of this type suitable for tiny transistoramplifier hearing aids, present critical. operating and, space limitations, and they require careful and relatively difficult assembly by specially trained, highly skilled personnel. i i Y Among the objects of the invention are miniature transducers of the foregoing type, embodying feat ures which materially simplify the assembly and assure properly aligned assembly of the tiny transducer components into the composite, efilciently operating transdu'cers, without requiring personnel of unusual skillv for their assembly. Among the objects of the invention are also miniature acoustic signaltransducers offthetore going type, which within 'a given transducer size will provide'superior response characteristics.

The foregoing and'other objects of the invention will be best understood from the following description of exemplifications thereof, reference being bad tothe aecompanying drawings, showing all parts greatly enlarged, wherein:

Fig. l is a cross-sectional view of an aconstiqdia phra'gm transducer of the invention, shown'witli some of the adjacent elements of a complete transistor amplifier hearing aid; i Fig. 1-A is an elevational view of a transistorp fie h ri g id s t s, uqtn by h use the casing of thehearing aid' enclosin p m rans w s hQWn in Fis EigI'Z is a transverse cross-sectional view of the transcer of 13 l Fig. 3. is. is o vi wv at he aassssssmf i w h. the diaphragm "and overlying easin -wan reniovedf 2,927,978 fatented Ma.

ice

- 0f the transdhcer winding;

Fig. 5-B is a cross-sectional view along line 5 B5-B of Fig."5-'-'A;

Fig, 7 is a top view assembly of the transducer;

Fig. 8 is a cross-sectional view. along line. of

ish; n I

Big. 9 is a top view of a spacing shim for the, transducer reed. i

In Fig. 1 shown an end view, of a complete transistor hearing aid the over-all dimensions of which are small enough to form a rear portion 10 of a temple 11 of an eyeglass frame 12 worn by the user, as seen in Fig. 1-A. The over-all dimensions of the casinglt) of the hearing aid unit are such that its volume may be given a shape so that it fits in its entirety- -together with the transistor circuits, battery and volume controlfa-within the concha cavity of the users ear between the tragns and anti-helix thereof, such as described, for instance, in the pending application of F. A. Hermann, Serial No. 705,841, filedDecember 30, 1 95.7, and assigned to the assignee of the present application. Within the. tiny casing 10 of such complete transistor-amplifier hearing aid are mounted both a microphonestransducer which transduces sound propagated in the'surrounding space into corresponding electric signals, and a receiver-transducer which transduces the amplified microphone signals into corresponding sound which is delivered to. the, ear canal of the user. Both the microphone. transducer and the receiver transducer have essentially the same transducer structures, and they will now be described in connection with the acoustic microphone transducer 20 which is shown suspended within the hearing-aid casing It} in Fig. 1, and also in Figs. 2-4.

The acoustic transducer 20 comprises a vibratory diaphragm 21 which is connected, through a driverodl 22, to a vibratory armature or reed 25 of an electromagnetic signal-transducer structure having a spool 31, with transducer windings 39 wound thereon, and 'a cooperating ferromagnetic core structure generally designated 40; The armature reed 25, is of low-retentivity, high-permeability ferromagnetic material, and is shown as being of fiat cross-section and extending with its flat surface in a plane perpendicular to the surface of Fig. 1.

The cooperating ferromagnetic core structure 40 comprises one pair of pole arms 41, 51 extending transversely across and spacedlfrom the opposite fiat surfaces of the left end portion 26 of the armature reed 25, and another pair of pole arms 43, 53. extending, transversely across and spaced from the opposite fiatsurfacesof the opposite end portion 29 of the armature reed 25. The pole-armpair 41, 51 has intermediate or central depressed or inwardly offset pole portions 42, 52 of opposite polarity portions 42, 52 of the ferromagnetic core structure The other pole-arm pair 3, 53 h s s milar en ral dep ssed po e portions ;"5- of opp i ol in V yN. and. s gns, wi h flat P0 1 1 'r y g 1' and substaiitially coextensive with the one 6 end areas of parts of the magnetic core of the other flat reed end 29, and positioned at a slight air gap spacing on opposite sides thereof so that flat reed end 29 is free to vibrate in the air-gap space between the two overlying opposite-polarity poles 44, 54 of the ferromagnetic core structure 40. The two pairs of pole arms 41, 51 and 43, 53 are shown formed of fiat sheet stock of low-retentivity, high-permeability ferromagnetic material, and their respective central poles 42, 52 and 44, 54 are given the desired opposite polarity by permanently magnetized core elements of the magnetic core structure 49. Although each of the two pairs of transverse pole arms 41, 51 and 43, 53, may form a distinct unit, the pole arms 41,:43 form two opposite integral arms of a generally rectangular ferromagnetic pole frame member 45 (Figs. 7 and 8), and the other two pole arms 51 and 53, which are of opposite polarity, form two opposite integral arms of a similarly shaped ferromagnetic pole frame member 55. The two pole frame members 45, 55 form upwardly and downwardly facing opposite frame parts of the magnetic core structure 49, as seen in Figs. land 2.

The desired permanent magnetic polarization and unidirectional field is maintained at the pole pair 42, 52 and the pole pair 44, 54 of the magnetic core, by two elongated permanent magnet members or bars 49 (Figs. 2 and 8) having opposite outer faces held clamped between the overlying inward clamping faces of the two side arms of the opposite pole frame members 45, 55 extending generally parallel to the reed 25, as seen in Figs. 1, 2 and 7, 8, and also in diagrammatic Fig.4. Each of the two permanent magnet bars 49 are magnetically polarized in a direction perpendicular to the flat surfaces of the overlying pole frame members 45, 55, as indicated by the N and S signs applied to the core bars 49 in Fig. l, and in the diagrammatic view of Fig. 4.

The armature reed 25 may be pivotally supported in any known manner at its central region so that when vibrated as a microphone part in opposite directions on its central pivot support, the two opposite reed ends 26, 29 will approach one set of opposite-polarity core poles 42, 54 in one half-cycle of each vibration cycle, and will approach the other set of opposite-polarity set of core poles 44, 52 in the opposite half-cycle of each vibration cycle. As the two opposite reed ends 26, 29 so approach in opposite vibration half-cycles, opposite-polarity core poles 42, 54 and 44, 52, respectively, the permanently magnetized core 49 will induce in reed 25 oppositelydirected magnetic fluxes, respectively, indicated by singlehead arrow 251 and double-head arrow 252 (Figs. 1, 4) and thereby generate corresponding oscillating electric signal currents in the surrounding transducer windings -39. When operating as a receiver, opposite halfcycles of oscillating current traversing the transducer windings 39 will induce in the reed 25 oppositely directed magnetic polarizing fluxes indicated by the two opposite arrows 25-1, 252,. As a result, the two alternately polarized reed ends 26, 29 will vibrate between the respective two sets of opposite-polarity core poles 42, 52 and 44,54, in accordance with their alternating polarization.

In the acoustic transducer shown, one reed end, namely reed end 26, is held clamped and fixed by central clamping screw 64 at a magnetic center position between the overlying opposite-polarity poles 42, 52 of the permanently magnetized core, so as to pivotally support the reed as for vibration with free reed end 29 in the air gap between opposite-polarity core poles 44, 54 (Figs. 1 and 2). When operating as a microphone, the acoustic diaphragm drive rod 22 vibrates the reed 25 in spool compartment 32, and the free reed end 29 will alternately approach the opposite-polarity core poles 44, 54 and similarly induce oppositely directed magnetic fluxes indicated by opposite arrows 251 and 252 in successive half-cycles of each complete vibration cycle and thereby generate correspond ing oscillating electric signal currents in the surrounding transducer windings. When operating as a receiver, with the clamped reed end 26 held fixed in the magnetic center between the overlying opposite-polarity core poles 42, 52, oscillating currents traversing the transducer windings 39 will induce in the armature reed 25, oppositely directed magnetic polarizing fluxes indicated by the opposite arrows 251, 252, thereby causing the free reed end 29 to vibrate in the air gap between its associated oppositepolarity core poles 44, 54 in accordance with the sequence of opposite polarizations imparted to the free reed end 29 during each opposite half-cycle of each complete reed vibration cycle.

In the transducer of Fig. 1, the opposite surfaces of the clamped, fixed reed end 26 are held spaced from the two opposite-polarity central pole portions 42, 52 of the core structure 4% by spacers or shims 61, 62, 63 so as to maintain the clamped pivot reed end 26 in the magnetic spacing center between the overlying opposite-polarity core poles 42, 52. When the transducer windings 39 of such transducer are not traversed by any direct current of the transistor-amplifier circuit, the magnetic spacing center coincides with the physical spacing center, and the clamped reed end 26 is held in the physical spacing center between the opposite-polarity core poles 42, 52 by non-magnetic spacer shims of non-magnetic metal, for instance, of the same thickness. When the transducer windings 39 of such transducer amplifier hearing aid are traversed not only by alternating signal currents, but also by a direct-current component of the amplifier circuits, suchdirect-current component imparts permanent directcurrent polarization to clamped reed end 26, thereby shifting the magnetic spacing center to a point other than the physical spacing center between the overlying opposite-polarity core poles 42, 52. In order to maintain the clamped reed end 26 clamped in' the true magnetic spacing center position betwen its overlying opposite-polarity core poles 42, 52, the clampedreed end 26 is shown held spaced fro-m core pole 52 by a nonmagnetic spacer shim 62 and a magnetic spacer shim 63, and the opposite side of the clamped reed end 26 is held spaced from the opposite-polarity core pole 42.by a nonmagnetic spacer shim 61 of non-magnetic material the thickness of which is chosen to assure that the clamped reed end 26, which is additionally polarized by direct current through the transducer coil 39, is held clamped and retained in a true magnetic spacing center between the opposite-polarity core poles 42, 52.

As indicated in Fig. 1, clamping screw 64 has a head overlying the outer surface of the depressed central core pole portion 42 of core arm 41, and it has a threaded rod or shank which passes through corresponding aligned openings of core pole 42, reed end 26 and spacing shims 61, 62, 63, and the threaded opening in similarly depressed central core pole portion 52 provides for proper, positive mounting and clamping engagement of the clamped reed end 25 at the proper magnetic center position between the core poles 42, 52. The other screws 65 passing through holes in opposite end portions of the other pairs of pole arms 43 and 53 of the two core frame members 45, 46, respectively, complete the clamping connections between the two pole frames 45, 55 across the two elongated permanent magnet bars 49 and join them into a relatively rigid unitary, self-supporting magnetic core structure 40.

The elongated spool member or spool 31 of the transducer windings 39 (Figs. 13 and detail Figs. 5 to S-B) has a flat cross-section corresponding to the cross-section of the reed 25 which it surrounds. The spool 31 has two flat spool walls 32 enclosing between them a flat central spool compartment 33 within which the major part of the reed 25 is positioned for vibratory motion in the spool compartment 3=3 in a direction transverse or perpendicular to the major surface of the reed and the spool walls 32. The spool 31 has two end walls 34 of a height corresponding to the height of the surrounding core structure 40, and side edges 35 which have fitting engagemeat withii-nward sideedg'es as of'th' 1 members 45, -55. Referring to *Fig.

s i. V w c s s 7 56.. .s i, i 7-, '8, the Ltwo-generally rectangular'core frame "members 45, 55-are'identical in shap'eand-in every-unaud ted,

and along its inward edge each *core name member 45,

-55"has inward side-arm edges 46,- four corners with corner edges 47, and two mess-arm edges-485 1, 4 842,

which-surround the frame space within wli-ichthe spool 31 with its transducer windings are'po'sitionedv The distance between the-opposite inward side-arm edges 46 of each pole frame member 45, SScorresPGnds to the distance between the side'edges 35 of thespool end walls 34, so as to receive with'ah aligning fit the l ateral edges 35 of the spool end walls 34 and positively fi'x' the'transsverse operating'centra'l 'spositi'o'nof the spool 31 between the side arms of the pole frame members 4 5*, The distance between the facing frame corner dges'47 which extend perpendicularly to the side frame edges 46, 'corre sponds to the longitudinal distance between the outer surfaces 36 of the spool end walls 34 so as to receive with an aligning fit and positivlylocat'e the'endsur'faces 36 of the spool end walls 34 and positively locate the longitudinal operative position of the spool 31.

In miniature acoustic signal transducers "of the present invention, where space limits are critical, the distance between the spool compartment walls 32 (Fig. 5-3) which define the operative compartment height across which the armature reed 25 vibrates, must be kept toa minimum. Thus, in a miniature transducer operating with a magnetic armature reed having a thickness of .010, it is desirable to keep the height of the spool compartment 33 or the distance between its fiat walls '32 to a minimum at which their inwardly facing surfaces will remain free from the slightest interference with the freely vibrating portions of reed 25 held between them. As-an eXample, in the specific transducer shown, it is desirable to keep the distance between the facing spool walls 32 at about .026:.O'Ol". 'The minutedimension tolerance of .001" in the height dimension of such spool is needed for enabling production of such spools on a practical basis, as by molding with a resin'with'out prohibiti-ve shrinkagelosses.

In assembling the components of such miniaturetransducer, critical problems are encounteredin the proper positioning of the spool 31 in relation to the core 40, for

assuring that the spool compartment walls 32 are at the proper critical distance from the opposite surfaces of the vibratory reed 25. Even with skilled operators, excessive production shrinkage is caused by failures in the required accurate positioning of the spool 31 with respect to the magnetic core 49, that would eliminate interference with the free reed vibrations 'in the assembled transducer, and avoid prohibitive shrinkage losses.

In accordance with the present invention, t hecr'itical difiiculties encountered in the accurate positioning of the spool compartment walls 32'rela'tively to the major surfaces of the vibratory reed 25 when assembling such miniature transducers, are substantially overcome by providing' the spool end walls 34 at a plurality of peripherally spaced regions thereof with outwardly extending align ing projections or members of a height corresponding exactly to the operative spacing of the two opposite pole frame members 45, 55, and arranged for aligning engagement with peripherally displaced portions of the assembled core frame members 45, 55. Since the spacing of the two pole frame members 45, 55 defines the spacing of their two sets of opposite-polarity pole pairs 42, 52 and 44, 54 and the magnetically centered operative position of the reed 25, such peripherally displaced aligning projections of the spool 31 make it possible to assure that in the assembly of the transducer components, the two spool compartment walls '32 are automatically positioned vibratory reed 25 extending therethrough.

V ienir w 11s t-reproduce'falongtts outward endwall 3' awe spaced outwardly projecting "spool "ialig' n'g uldfs ofr'projectious 37 extending parallel to the di ctionof the'vibratory rnetion of the 'reed'z's. acho'f t e four spool aligning'projections 37 has a pair 6faccurately pesitionednansverse spool aligning surfaces 38 whichde'fiirie the height 'at which the assembled core pole frarjnes 45, 55 are "engaged by them so as to assure that they are placed in the accurate operative position wherein the central'spool compartment'walls 32 remain free "from ntferterin'gengagement with the'vibrato'ry reed 25 passing spool aligning surfaces "38 is identical with the spacing of the facingfupper and lower "surfaces of the permanent magnet cor'e'bar's 49 (as seen in Figs. 1 and '3) which are held clamped between the two core frame members 45, 55 The ion "alignin'g'proj'ections 37 of the spool il'are located t rear peripherally displaced outward portions of the pool sfructu're 31, thereby assuring that the four aligning shoulders 37 '1 en age four peripherally displaced cooperatingali' g surfaces. at the four corners of each of the two outer "co're'poleframes 45, 5'5, and enable 'accuratejaligned positioning and assembly of the core elements T45, '55, 49, the spool 31 and the read 25 into the composite, operative transducer unit 40 shown. By providing'the tiny spool 3Lwith the four peripherally displaced Iali lnfg shoulders 37 along the outward sur-' faces ofjthe spool en'dwalls 34, th'eass'embly and accurate positioning of the spoolwith the other elements of thercomposite transducer structure is thus greatly simplifie'd, By way of example, such assembly may be performed as follows: 7

In a "suitabIejig therje-is first'po'sitioned the lower core pole frame, 55. After placing on the transverse core pole '52 the 'pro per lower spacing shim or shims, such asspacing shims 62, 63, the reed 25 withthe spool 31 and the transducer winding 39 previously positioned over the read, are dropped into the jig'which aligns them inrtheir proper positions with the spool end walls 34 fitting between the-'two inward side edges 46 andthe four corner edges 47 of the lower corefrarne 55 This brings '31 (as seen in Figs.;1, '2, 5) in aligning contact engagement withfour peripherally spaced aligning corners 47 of the 'lowerpo'le frame 55. Thereupon the upper shim, such as shim 61, is placed over the to-be clamped reed end 26 and the two permanent magnet cores 49 are place d along the side arms of the lower pole frame member 55 within the assembly jig. Thereafter, the upper pole frame member 45 is placed 'in'the'jig whereinit is automatically aligned over' the component assembly, in which position the inwardly facing surfaces of the fourinn'er corners 47 ofsth'e upper frame 45 automatically come into aligning, engagement with the peripherally displaced upwardly facing spool aligning surfaces 38 ofthe fourspool aligning projections 37, thereby automatically assuring that the spool 31 with its closely spaced compartment walls 32 will be'properly aligned with respejct to the two core pole frame 'members 45;"55 and therethrough with respect to the vibratory transducer reed 25. The assembly is completed by screwing in position the three clamping screws 64, '65 which join the assembly into the operative transduc'er unit. n I Y :The outwardly extending aligning spool projections. 37' do not increase the. over-all dimensions of the transducer assembly because the spool-aligning projections 37' merely occupy space available 'at the four inner corner; regions *of the generally rectangular core assembl'y of th'e transducer. The aligning spool projections 37 also make it possible to provide spool body "31 around which'th transducer win gs are weund, wit'h the re quired' trig ityLWhile' reducing to a minimum the lateral space occupied by the was of the spool compartme'rit 33, as seen in Figs. 1-5 and 'S -B. The reduction of the herethro'u'g'h. The spacing of each pair of lateral space occupied by the walls of the spool compartment 33 of the winding spool 31 is secured by eliminating the side walls of the spool compartment and utilizing as '32 are not deformed under strain and are maintained at the correct spacing of the spool compartment 33 free of interfering engagement with vibrating portions of the armature reed 25.

In miniature transducers of the foregoing type, it is desirable to utilize highly permeable ferromagnetic material, for instance the material known as Hymu 80, for the resilient, vibratory reed 25. The limitations on the minimum required cross-section and on the length of the vibratory reed 25, make it difiicult to obtain a reed of such highly permeable magnetic material which will operate with the compliance required for optimum transducer sensitivity. In accordance with the invention, the vibratory ferromagnetic reed is given the desired greater compliance within the required minimum length and thickness dimensions, by arranging the clamping connection of the clamped reed end 26 in such manner as to permit free vibration of a part of the clamped reed end 26 which would normally be held clamped and restrained against vibration. The novel arrangement of the clamped reed end 26 which increases the free vibrating length of the reed, while assuring that the clamped reed end is properly maintained in its clamped operative position, will now be described (Figs. 1, 2, 6 and 9).

In the accepted prior-art practice, the spacing shims 61, 62, 63 with which the reed was held clamped between the facing pole portions 42, 52 of the two pole frames 45, 55, normally extended over the entire area of the reed end 26, which is embraced by the two pole portions 42, 52, of core frames 45, 55. In accordance with the invention of Harry A. Pearson, assigned to the assignee of the present application, the dimensions of the spacing shims, and particularly of the non-magnetic shims 61, 62 overlying the clamped reed end 26, are limited along the longitudinal direction of the reed 25 only up to at most three-quarters of the reed area embraced by the core poles 42, 52. In the arrangement shown, the two spacer shims 61, 62 have the shape shown in Fig. 9. Each shim, such as shim 61, has two arms extending from its outer edge along both sides of the fastening member or clamping screw or rod 64 to the inward edge of the screw opening 612 through which the clamping screw 64 passes. The so-formed shims 61, 62 of the clamped reed end 26 confine the clamping engagement to the outward edge region of the clamped reed end and two rear portions of the adjoining reed mounting portion embracing the clamping screw 64 which are in clamping engagement with the inner edge 61-2 of the adjacent overlying spacing shims 61, 62. In addition, the'part of the clamped reed end 26 with the reed opening 261 (Fig. 6) through which the screw 64 extends, is enlarged in the adjoining inward reed region extending beyond the overlying inner spacer shim edges 612, thereby providing the free inward reed portions adjoining the clamped reed end 26 with two flexible resilient reed junction arms 254 having a radial dimension shorter than the radial dimension of the adjoining reed portions which are held clamped between the shims 61, 62. This makes it possible to give the reed 25 the desired greater compliance and secure operation thereof with the desired resonant mode at which the acoustic transducer will operate with desired over-all response.

Circuit connections from the coil winding 39 to cooperating'exterior surfaces may be provided in any conventionalway; When used as a part of a compact hearing-aid, the connections to the windings 39 are provided by two flexible wire conductor leads 56 which are covered by an insulating coating layer and pass through an opening in a rim side wall of transducer casing 71, with the opening being sealed as by cement so as'to retain therein the conductors 56 and keep the lead opening sealed. The internal ends of the two insulated conductor leads 56 are stripped of their insulation and are electrically aflFixed, as by solder, to two spaced metallic transducer terminals 57, to which the transducer windings 39 are connected. The transducer terminals 57 are mounted on an underlying insulating terminal support which is mounted on the transducer unit 40. The insulating support for the transformer terminals 57 may be formed of overlapping layers of insulating sheet material, for instance resin-impregnated cloth, holding between them one leg of two tiny U-shaped terminals 57, leaving one terminal leg 57 exposed for connection to the stripped conductor lead ends 56.

Miniature acoustic transducers of the type described herein, usually also have a casing or cup 71 of suitable metal, for instance, brass or aluminum, within which the transducer assembly is mounted. The transducer structure is suitably afiixed to the casing 71, for instance, as by placing four drops 73 of cement along spaced peripheral regions of the upwardly facing core frame member 45 Where it adjoins the casing side Walls 72 (\Fig. 3). The casing 71 has side walls or a rim 72 with a rim edge to which the edge of diaphragm 21 is secured, as by cement. The casing '71 may be of magnetic shield material, where it is desired to magnetically shield the electromagnetic elements of the transducer against magnetic interliukage with disturbing magnetic fields of another similar transducer, for instance, for suppressing magnetic feedback interlinkage between the electromagnetic elements of a microphone transducer and receiver transducer forming parts of a transistor hearing aid. The casing 71 may be made of a non-magnetic metal, and where a shield enclosure is desired, an outer magnetic shield casing or cup 74 is placed in contact with and over the interior housing cup 71. A cover wall '75 of metal, overlying the exterior side of the vibratory diaphragm 21, has a rim which is joined, as by cement, to the casing 72. Acoustic excitation of the diaphragm 21 or delivery of generated sound, may be obtained by providing the casing cover 75 with one or more acoustic openings.

After the internal transducer unit 40 is assembled in the casing 71 and before the diaphragm 21 is afiixed thereto and to the casing, the operative position of the vlbratory reed 25 is checked to assure that it is in the magnetic center between the adjacent poles 42, 52 of the core structure. Although proper choice of the magnetic shim in relation to the magnitude of the direct-current traversing the coil windings 39 will secure proper magnetic centering of the mounting end 26 of the armature reed, additional minute adjustment of the reed position is desirable to assure optimum operation of the transducer. Such minute adjustment of the reed 25 may be eifected by applying to the upper or the lower side of the reed 25, as seen in Fig. l, the tip of a bending pin or rod for giving it a minute permanent bend in one or the other direction to bring the reed 25 to its optimum operating position. The optimum operating position may be checked by connecting the transducer windings to an instrument, for instance an oscilloscope, and observing the responseof the transducer unit 46 over a critical frequency range thereof. setting tool may be applied to the portion of the reed 25 which is exposedin the transducer unit 40 between the inward edge of the core-pole pair 42, 52 and the ad- In the transducer shown, such iheent spoolend walls f34,, as,;see'n to thezleftzin Figs. 1

' and .3, the tool :bjeing appiied :in. the directiongof zone .of

the arrows 66. .-In order 'to-make itpossible -for such setting toolto be applied to thereed in the directionzof I arrows 66 while assembled-in .-casing.7-1,this casing .and

phone, is shown suspended inthe interior of the hearing aid casing 10 so as to suppress transmission of vibrations between the transducer and the outer casing 10 and the other similarly suspended acoustic transducer, such as the receiver mountedin the hearing-aid casing it). Such vibration-suppressing suspension may be provided by generally Z-shaped suspension members 10-2 of vibration-damping sheet material, such was elastorner material, having opposite end tongue portionsas ecured to theouter surface portions .of the transducer casing 71 and the hearing-aid casing 10, respectively, in which it is carried. i

The acoustic responses .of a transducer of-the type described above, are controlled by the acousticcharacteristics of the interior transducer compartment 69 bounded by the inner side of diaphragm 21 and casing 7:1,and of the'outerdiaphragmcompartment 76 bounded'by the outer side of diaphragm 21 and the outer casing cover '75. In the transducer .shown, the acoustic connection from the outer diaphragm compartment 76 .to the exterior space (in the case of a microphone) or to the ear canal (in the case of a receiver), is provided byv a sound channel or passage 77 extending along'thecasing rim Wall 72 of the casing 71. In accordance with the invention, the side rim 'wall 72 of easing 71 is formed with an inwardly recessed channel-shaped wall portion 81 vextending from the level of the diaphragm 21 .to an'inward wall level, and a cover wall ,821iS afiixed, 'as bycement or solder, to the recessed channel-shaped wall portion 81 of casing rim 72 to form the desired soundgchannel 77 between the outer diaphragm compartment 76 and the exterior space. A cover -wall opening ;83 connects :the sound channel'77 to' the exterior space. Thenvibratory diaphragm 21 overlying the upper endzofthe sound channel 77 (as seen in Fig. 1) hasza-nopening 21-1 through which the channel passage 77iis connected to the diaphragm front compartment 76, thereby completing an acoustic connection from the exterior space to the outer diaphragm compartment space 76. In the case of a hearingaid, the channel opening 83 of the sound channel 77 is suitably connected either to the exterior space when operating as a microphone for exciting the diaphragm by exterior sound, or to .the ear canal of the user for delivering or propagating the sound-generated in the front diaphragm compartment 76 to the ear canal of the user. In Fig. 1, the transducer is shown operating as a microphone which is excited by sound propagated from the exterior space through sound channel 77.

The sound channel opening 83 of the sound passage 77. is connected to a casing opening 101 of the hearingaid casing through a coupling channel 85 (Fig. 1') for the transmission of sound propagated in the surrounding space through casing opening 10-1, sound passage 86 of coupling channel 85, sound channel opening 83, and through sound channel 77, into the outer diaphragm compartment 76 for exciting the diaphragm 21 and cause it to generate corresponding signals in the transducer windings 39. The coupling channel 85 may ,be made of elastomer material, and has one end surface sealingly engaging the surface of the casing 10' surrounding casing opening 104. The opposite end surface of coupling channel :85 seaiingly-engagesthe facing :opening .83 er soundrpassagefi 10f casing rim 72.

The'acousticpassage73 formed bytthe recessed-casing wallportion 81 through'which the outer transducer di phragm compartment 76 is connected tov the exterior space, is dimensioned so that it provides an acoustic impedance aWhiCh lowers the resonant frequency of the transducer and thereby enhances the response of the ;re ceiver over the lower frequency range. Thus, in the specific form 'of transducer shown, the acoustic passage connection '77 ;froin the outer diaphragm compartment 76 to theexteriorspace is dimensioned to provide an acoustic mass impedance which lowers the resonant frequency of the transducer system from about 2000 c.p.s. (cycles persecond) to 1400 c.p.s., or in general, to a resonant frequency in the'range between 1300 c.p;s. and'l500 c.p.s. Such acoustic passage connection to the exterior space may be readily designed, as byv restricting its cross-section over a specified length thereof, for raising its acoustic resistance and thereby damp the peaked transducer response at its resonant frequency.

By forming the acoustic passage connection from the outer diaphragm compartment'to the exterior space with.

a recessed casing wall channel of the transducer casing rim, the sound connection to the surrounding space is provided along a side wall or rim of the transducer casing. Such acoustic connection along the relatively short side wall of the transducer casing eliminates the problems encountered in miniature all-in-one hearing aids when making an acoustic connection to the diaphragm compartment openings of .an acoustic transducer through an opening in a casing such as casing Wall 75 overlying the diaphragm 21.

In accordance with'a phase of the invention, such inwardly recessed channel-shaped wall portion of the transducercasing, such as transducer casing 71, is utilized in conjunction with an outer cover portion such as cover wall 82 to provide a sound passage of predetermined acoustic characteristics through which one of the trans ducer compartments is connected either to the exterior space or to another transducer compartment and thereby modify or control the acoustic response of the trans-J ducer over a predetermined frequency range. In addition, such acoustic channel passage or restricted crosssection may be used, for instance, in the manner .described in Knauert Patent 2,820,107, for raisingthe frequency response of a microphone between .200 and 600 c.p.s. In the transducer. shown, the inner transducer compartment 69 has connected thereto a restricted sound passage of predetermined impedance which forms with the space of the interior transducer compartment an acoustic system.

There will now be described one manner in which an acoustic passage channel formed byan inwardly-recessed, channel-shaped wall portion of transducer casing 71, is utilized for similarly raising the frequency response of a microphone in the low-frequency range, for instance between 400 and 600 c.p.s., or in general, between 200 and 600 c.p.s.

Inthe transducer shown, the-recessed portion of rim side wall 72 of the transducer which forms with casing cover wall 82 the recessed sound channel 77, has further recessed channel Wall portions 91 and 92 which form with casing cover wall 82 an additional sound passage 93 which connects sound channel 17 to the interior transducer compartment 69. The recessed wall portion 92 of the additional acoustic channel or passage 93 has an acoustic opening 94 below the level of the diaphragm 21,

through which the space of additional sound passage 96.

is acoustically connected to the inner transducer compartment 69. The acoustic impedance of the additional channel passage 93 and its opening connection 94 to the inner transducer compartment 69, is designed to have a predetermined impedance which will form in conjunction with the acoustic'space of the inner transducer compartment 69 an acoustic system which resonates, for instance, at

400 or 500 c.p.s. (cycles per second), for thereby raising the frequency response of the microphone in this frequency range, in a manner similar to that explained in the referred-to Knauert patent. In a similar way, other wall portions of the transducer casing 71 may be provided with recessed channels for forming acoustic passages connected to an acoustic compartment of the transducer for modifying or controlling the response of the transducer in a selected part of its frequency range.

The cover wall 82 which forms with the recessed channel-shaped portions of casing rim wall 72, the sound channels 77 and 93, described above, may be of a di mension just sufiicient to slightly overlap the width of the passage, the cover wall portion 82 being secured to the underlying wall portion of the casing rim wall 72,

as by cement or solder. In the arrangement shown, a

single cover wall member 82 is secured to the recessed channel-shaped wall portions 81, 92, of the casing side wall, for forming therewith the two sound passages 77 and 93. Where the microphone casing 71 is provided With a magnetic shield, cover wall 82 may be formed of ferromagnetic high-permeability material and may form part of the magnetic shield 74 seated over the inner casing wall 81 and forming a magnetic shield enclosure around it.

By way of example, there are given below, construction data of a practical embodiment of the invention in the form of a miniature microphone transducer of a heating aid:

Reed.--HYMU 80 magnetic material; .010" thick; .300"

long; .100" wide, with mounting end .135" wide. Diameter of reed opening .021" to .047"; width of two reed arms beyond reed opening .037" to .050" depending on desired response.

Cut-off spacer shim for reed.-Brass; thickness either 0.002; 0.003"; 0.0035"; 0.004", depending on desired response. Distance from opening center to rear edge, .040, and to shorter front edge .010".

Permanent magnet cores.Alnico 2; .330" long; .070"

in height; .067" width.

Pole arm frames.Alloy of 50% N, 50% Fe; .025 thickness; .080" pole arm width; .055" side arm width; .215" spacing of inner side arm edges; .218" spacing of inner pole arm edges.

Spool.-Nylon; .150" total length; .009" thickness; .115"

height; .188 width of reed compartment; .009" thickness of compartment side walls; .026 height and .118" width of reed compartment; .009" thickness of compartment side walls.

Spool-aligning projections.--.070" height transverse to reed; .016 projection length and end area width.

Main casing.-.008" wall thickness; .170" inside height; .436" by .336" inside area; .021" channel-recess depth, and .042 channel recess Width.

Aluminum foil diaphragm..0005" foil thickness of receiver; .0007" thickness of microphone.

The claims of the present application are directed to a miniature-size electromagnetic acoustic transducer device with an elongated vibratory magnetic reed, wherein the coil spool within which the reed vibrates has end walls with aligning projections fitting between the pole arms of the core assembly surrounding the reed and the coil, thereby assuring automatic alignment of the miniature components of the device in their critical operative posi-.

tions when assembled into an operative unit. Other features of invention disclosed herein constitute the subjectmatter of the co-pending applications, Serial No. 774,437. filed by W. F. Knauert on November 17, 1958, and Serial No. 774,439, filed by Harry A. Pearson, on November 17, 1958, and assigned to the assignee of the present application.

It will be apparent to those skilled in the art that the novel princples of the invention disclosed herein in con nection with specific exemplifications thereof will suggest various other modifications and applications of the same. It is accordingly desired that in construing the breadth of the appended claims, they shall not be limited to the specific exemplifications of the invention described above.

Iclaim: I

1. In an electromagnetic acoustic transducer device, an elongated flat ferromagnetic reed arranged to vibrate transversely to its flat areas between two opposite end positions and having two reed ends, a hollow spool memher having two opposite spool end walls at its opposite ends and an elongated interior space of a cross-section slightly larger than that of the reed in which the major length of said reed is held for vibration therein in a direction transverse to the flat reed area, transducing windings surrounding and held by said spool member, a ferro magnetic core structure comprising tWo elongated core bodies extending parallel along opposite sides and confining between them said spool member and one pair of ferromagnetic pole-arms extending transversely to and on opposite sides of each of the two flat reed ends between said two elongated core members and forming therewith two substantially closed ferromagnetic core return paths of opposite polarity in the opposite end posi tions of said reed and thereby causing vibratory motion of said reed to generate corresponding electric oscillations in said windings and vice versa, each spool end wall having two opposite outward aligning projections extending along opposite side edges of said reed in a direction transverse to its fiat reed area towards the adjoining pair of overlying pole-arms, each of said aligning projections having two opposite aligning surfaces facing and engaging opposite facing surface portions of the overlying polearms for thereby fixing the operative position of said spool member relatively to said core and said reed.

2. In a transducer device as claimed in claim 1, one end of said reed being clamped between one pair of said pole-arms and the other end of said reed being held free for vibratory motion in a narrow gap spacing between the other pair of said pole-arms.

3. In a transducer device as claimed in claim 1, a vibratory diaphragm having an intermediate portion connected to said reed for transmitting vibrations therebetween, an inner casing section having a rim wall surrounding an inner casing compartment, the peripheral region of said diaphragm being joined to said rim wall for enclosing said reed said core structure and said windings in said inner compartment, an outer casing section overlying the outer side of said diaphragm and forming with it a front compartment, said rim wall having an inwardly recessed channel-shaped wall portion extending from the level of said diaphragm to an inward level spaced from said diaphragm, a cover Wall overlying and afiixed to said channel-shaped wall portion and forming therewith a sound channel extending from said diaphragm to said inward level, said cover wall having in the region of said inward level a cover opening acoustically connecting said channel to the exterior space, said diaphragm having a diaphragm opening through which said front compaltment is acoustically connected to said sound channel and therethrough to the exterior space for propagation of sound between said front compartment and the exterior space.

4. In a transducer device as claimed in claim 3, said rim wall having a further recessed channel-shaped rim wall portion extending from the region of said cover opening to a further rim wall portion peripherally displaced from the cover-opening region, a further cover wall portion overlying and affixed to said further channelshaped rim wall portion and forming therewith a further sound channel extending from the region of said rim cover opening to said further rim wall portion, said further rim wall portion having a rim opening acoustically joining said further sound channel and said interior compartment into an acoustic system which resonates within 13 a selected frequency range between 200 and 600 cycles per second for raising the response of said transducer device over a region of said selected frequency range.

5. In .a transducer device as claimed in claim 4, one end of said reed being clamped between one pair of said pole-arms and the other end of said reed being held free for vibratory motion in a narrow gap spacing between the other pair ofvsaid pole-arms.

6. In a transducer device as claimed in claim 3, one endor said reed being clamped between one pair of said pole-arms and the other end of said reed being held free for vibratory motion in a narrow gap spacing between the other pair of said pole-arms.

7. In a transducer device as claimed in claim 1, the

relatively wide opposite side areas of the interior space of said spool member in which the reed vibrates being bounded by two solid spool side walls forming the spool body which is surrounded by said transducer windings,

said side walls having inwardly facing flat wall surfaces overlying the reed, said spool body having side openings 

